Fungicidal carbamate compounds

ABSTRACT

A compound of the formula: ##STR1## useful as a fungicidal agent against phytopathogenic fungi, and particularly the strains resistant to benzimidazole, thiophanate and/or cyclic imide fungicides.

This invention relates to fungicidal aniline derivatives.

Benzimidazole and thiophanate fungicides such as Benomyl(methyl 1-(butylcarbamoyl)benzimidazol-2-ylcarbamate), Fubelidazol(2-(2-furyl)benzimidazole), Thiabendazole(2-(4-thiazolyl)benzimidazole), Carbendazim(methyl benzimidazol-2-ylcarbamate), Thiophanate-methyl(1,2-bis(3-methoxycarbonyl-2-thioureido)benzene), Thiophanate(1,2-bis(3-ethoxycarbonyl-2-thioureido)benzene), 2-(O,S-dimethylphosphorylamino)-1-(3'-methoxycarbonyl-2'-thioureido)benzene and 2-(O,O-dimethylthiophosphorylamino)-1-(3'-methoxycarbonyl-2'-thioureido)benzene are known to shown an excellent fungicidal activity against various plant pathogenic fungi, and they have been widely used as agricultural fungicides since 1970. However, their continuous application over a long period of time provides phytopathogenic fungi with tolerance to them, whereby their plant disease-preventive effect is much lowered. Further, the fungi which gained tolerance to certain kinds of benzimidazole of thiophanate fungicides also show considerable tolerance to some other kinds of benzimidazole or thiophanate fungicides. Thus, they are apt to obtain cross-tolerance. Therefore, if any material decrease of their plant disease-preventive effect in certain fields is observed, their application to such fields has to be discontinued. But, it is often observed that the density of drug-resistant organisms is not decreased even long after the discontinuation of the application. Although other kinds of fungicides have to be employed in such case, only few are so effective as benzimidazole or thiophanate fungicides in controlling various phytopathogenic fungi. Cyclic imide fungicides such as Procymidone(3-(3',5'-dichlorophenyl)-1,2-dimethylcyclopropane-1,2-dicarboximide), Iprodione(3-(3',5'-dichlorophenyl)-1-isopropylcarbamoylimidazolidine-2,4-dione), Vinchlozolin(3-(3',5'-(dichlorophenyl)-5-methyl-5-vinyloxazolidin-2,4-dione), ethyl(RS)-3-(3',5'-dichlorophenyl)-5-methyl-2,4-dioxooxazolidine-5-carboxylate, etc., which are effective against various plant diseases, particularly those caused by Botrytis cinerea, have the same defects as previously explained with respect to the benzimidazole or thiophanate fungicides.

In C.R. Acad. Sc. Paris, t. 289, Serie D, pages 691-693 (1979), it is described that such herbicides as Barban (4-chloro-2-butynyl N-(3-chlorophenyl)carbamate), Chlorobufam(1-methyl-2-propynyl N-(3-chlorophenyl)carbamate), Chloropropham(isopropyl N-(3-chlorophenyl)carbamate) and Propham(isopropyl N-phenylcarbamate) exhibit a fungicidal activity against certain organisms tolerant to some of the benzimidazole or thiophanate fungicides. However, their fungicidal activity against the drug-resistant fungi is not strong enough, and hence, practically they can not be used as fungicides.

As a result of a study seeking a new type of fungicides, it has now been found that aniline derivatives of the formula: ##STR2## wherein R₁, R₂ and R₃ are, the same or different, each a lower alkyl group; X is a halogen atom, a lower alkyl group or a lower alkoxy group; and A and B are, the same or different, each an oxygen atom or a sulfur atom, show an excellent fungicidal activity against plant pathogenic fungi which have developed resistance to benzimidazole, thiophanate and/or cyclic imide fungicides. It is notable that their fungicidal potency against the organisms tolerant to benzimidazole, thiophanate and/or cyclic imide fungicides (hereinafter referred to as "drug-resistant fungi" or "drug-resistant strains") is much higher than that against the organisms sensitive to benzimidazole, thiophanate and/or cyclic imide fungicides (hereinafter referred to as "drug-sensitive fungi" or "drug-sensitive strains").

In view of their excellent fungicidal properties, particularly useful are the compound of the formula (I) wherein R₁ and R₂ are each a lower alkyl group, R₃ is an isopropyl group, X is a fluorine atom and A and B are each an oxygen atom.

The aniline derivatives of the formula (I) are fungicidally effective against a wide scope of plant pathogenic fungi, of which examples are as follows: Podosphaera leucotricha, Venturia inaequalis, Mycosphaerella pomi, Marssonina mali and Sclerotinia mali of apple, Phyllactinia kakicola and Gloeosporium kaki of persimmon, Cladosporium carpophilum and Phomopsis sp. of peach, Cercospora viticola, Uncinula necator, Elsinoe ampelina and Glomerella cingulata of grape, Cercospora beticola of sugarbeet, Cercospora arachidicola and Cercospora personata of peanut, Erysiphe graminis f. sp. hordei, Cercosporella herpotrichoides and Fusarium nivale of barley, Erysiphe graminis f. sp. tritici of wheat, Sphaerotheca fuliginea and Cladosporium cucumerinum of cucumber, Cladosporium fulvum of tomato, Corynespora melongenae of eggplant, Sphaerotheca humuli, Fusarium oxysporum f. sp. fragariae of strawberry, Botrytis alli of onion, Cercospora apii of celery, Phaeoisariopsis griseola of kidney bean, Erysiphe cichoracearum of tobacco, Diplocarpon rosae of rose, Elsinoe fawcetti, Penicillium italicum, Penicillium digitatum of orange, Botrytis cinera of cucumber, eggplant, tomato, strawberry, pimiento, onion, lettuce, grape, orange, cyclamen, rose or hop, Sclerotinia sclerotiorum of cucumber, eggplant, pimiento, lettuce, celery, kidney bean, soybean, azuki bean, potato or sunflower, Sclerotinia cinerea of peach or cherry, Mycosphaerella melonis of cucumber or melon, etc. Namely, the compounds of the formula (I) are highly effective in controlling the drug-resistant strains of said fungi.

The compounds of the formula (I) are also fungicidally effective against fungi sensitive to said known fungicides as well as fungi to which said known fungicides are ineffective. Examples of such fungi are Pyricularia oryzae, Pseudoperonospora cubensis, Plasmopara viticola, Phytophthora infestans, etc.

Advantageously, the compounds (I) are of low toxicity and have little detrimental actions on mammals, fishes and so on. Also, they may be applied to the agricultural field without causing any material toxicity to important crop plants.

Thus, the present invention provides a fungicidal compound of the formula (I) and a fungicidal composition which comprises, as an active ingredient, a fungicidally effective amount of the compound of the formula (I) and an inert carrier or diluent. It also provides a combination composition comprising as active ingredients the compound of the formula (I) together with a benzimidazole, thiophanate and/or a cyclic imide fungicide, which is fungicidally effective against not only drug-sensitive fungi but also drug-resistant fungi, and hence particularly effective for the prevention of plant diseases. It also provides a method of controlling plant pathogenic fungi including drug-resistant strains and drug-sensitive strains applying a fungicidally effective amount of the compound of the formula (I) to plant pathogenic fungi, and a process for producing the compound (I).

The compound of the formula (I) can be prepared by any one of the following procedures:

Procedure (a):

The compound (I) can be prepared by reacting a compound of the formula: ##STR3## wherein R₁, R₂ and X are each as defined above, with a compound of the formula: ##STR4## wherein R₃ and A are each as defined above and R₄ is a halogen atom.

The reaction is usually carried out in the presence of an inert solvent (e.g. benzene, toluene, tetrahydrofuran, chloroform, ethyl acetate, dimethylformamide). If desired, the reaction may be performed in the presence of a base (e.g. triethylamine, sodium hydroxide or sodium hydride) so as to obtain the compound (I) in a high yield. The reaction may be accomplished at a temperature of 30° to 120° C. instantaneously or within 12 hours.

Procedure (b):

The compound (I) can also be prepared by reacting a compound of the formula: ##STR5## wherein R₁, R₂, X and A are each as defined above, with a compound of the formula:

    H--B--R.sub.3                                              (V)

wherein B and R₃ are each as defined above.

The reaction is usually carried out in the absence or presence of an inert solvent (e.g. benzene, toluene, xylene, diethyl ether, tetrahydrofuran, dioxane, dimethylformamide, chloroform, carbon tetrachloride). If desired, the reaction may be performed in the presence of a catalyst (e.g. triethylamine, N,N-diethylaniline, 1,4-diazabicyclo[2.2.2]octane) so as to obtain the compound (I) in a high yield. The reaction may be accomplished at a temperature of 0° to 50° C. instantaneously or within 10 hours.

The starting compound (IV) in the above reaction can be prepared by reacting the compound (II) with phosgene or thiophosgene.

The reaction is usually carried out in the presence of an inert solvent (e.g. benzene, toluene, xylene, ethyl acetate). The reaction may be accomplished at a temperature of 50° C. to the boiling point of the solvent instantaneously or within 10 hours.

The starting compound (II) is obtainable by reducing a nitrobenzene derivative of the formula: ##STR6## wherein R₁, R₂ and X are each as defined above according to a conventional reduction procedure. In the case of a catalytic hydrogenation, for example, the reaction may be carried out in an inert solvent (e.g. ethyl acetate, ethanol) in the presence of a catalyst (e.g. platinum oxide, palladium on carbon) at a temperature of 0° to 60° C. under hydrogen gas at an ordinary or an elevated pressure.

The nitrobenzene derivative may be prepared by nitration of a catechol derivative of the formula: ##STR7## wherein R₁, R₂ and X are each as defined above, for instance, in an acetic acid or an acetic anhydride with a nitric acid (d is 1.38 to 1.52).

The catechol derivative is obtained by reacting a phenol derivative of the formula: ##STR8## wherein R₁ is as defined above, with a compound of the formula:

    R.sub.2 --R.sub.5

wherein R₂ is as defined above and R₅ is a leaving group such as a halogen atom and a tosyloxy group, or with a dialkyl sulfate of the formula:

    (R.sub.2).sub.2 SO.sub.2

wherein R₂ is as defined above.

The reaction may be carried out in an inert solvent (e.g. N,N-dimethylformamide, dimethylsulfoxide, tetrahydrofuran, dioxane) in the presence of a base (e.g. sodium hydroxide, potassium carbonate, sodium hydride) at a temperature of 0° to 100° C. instantaneously or within 12 hours.

The phenol derivative is per se known and may be prepared, for example, according to the method as described in J.Org.Chem., 46, 203-206 (1981).

Some typical examples for preparation of the compound (I) are illustratively shown below.

EXAMPLE 1 (according to Procedure (a))

2-Fluoro-3,4-diethoxyaniline (0.17 g) and N,N-diethylaniline (0.13 g) were dissolved in toluene (15 ml). To the resultant solution was dropwise added isopropyl chloroformate (0.11 g) in 5 minutes under ice-cooling. The resultant mixture was allowed to stand at room temperature for 12 hours, poured into ice-water and extracted with ethyl acetate. The extract was washed with water, dried over magnesium sulfate and concentrated under reduced pressure. The residue was purified by silica gel chromatography using a mixture of toluene and ethyl acetate as the eluent to give isopropyl N-(2-fluoro-3,4-diethoxyphenyl)carbamate (Compound No. 1) (0.23 g) in a yield of 94.4%. M.P., 79°-81° C.

Elementary analysis: Calcd. for C₁₄ H₂₀ FNO₄ : C, 58.92%; H, 7.08%, N; 4.91%. Found: C, 58.95%; H, 7.27%; N, 4.80%.

EXAMPLE 2 (according to Procedure (a))

In the same manner as in Example 1, there was obtained isopropyl N-(2-ethyl-3,4-diethoxyphenyl)carbamate (Compound No. 2) in a yield of 68%. M.P., 113.5°-115° C.

EXAMPLE 3 (according to Procedure (b))

2-Fluoro-3,4-diethoxyaniline (1.99 g) in toluene (20 ml) was dropwise added to a toluene solution containing 10 g of phosgene at 10° to 20° C. The resulting mixture was gradually heated and, after being refluxed for 30 minutes, cooled to room temperature. The solvent was removed by distillation under reduced pressure to give 2-fluoro-3,4-diethoxyphenyl isocyanate. The thus obtained crude substance was added to a toluene solution (50 ml) containing triethylamine (1.0 g) and isopropanol (1.0 g). The resultant mixture was allowed to stand at room temperature for 12 hours, poured into ice-water and extracted with ethyl acetate. The extract was washed with water, dried over magnesium sulfate and concentrated under reduced pressure. The residue was purified by silica gel chromatography using a mixture of toluene and ethyl acetate as the eluent to give isopropyl N-(2-fluoro-3,4-diethoxyphenyl)carbamate (Compound No. 1) (1.99 g) in a yield of 69.8%.

According to either one of Procedure (a) or (b), the aniline derivatives of the formula (I) as shown in Table 1 can be prepared.

                  TABLE 1                                                          ______________________________________                                          ##STR9##                                                                      Com-                                                                           pound                                                                          No.   R.sub.1  R.sub.2     X      A   B   R.sub.3                              ______________________________________                                         1     C.sub.2 H.sub.5                                                                         C.sub.2 H.sub.5                                                                            F      O   O   i-C.sub.3 H.sub.7                    2     C.sub.2 H.sub.5                                                                         C.sub.2 H.sub.5                                                                            C.sub.2 H.sub.5                                                                       O   O   i-C.sub.3 H.sub.7                    3     C.sub.2 H.sub.5                                                                         C.sub.2 H.sub.5                                                                            Cl     O   O   i-C.sub.3 H.sub.7                    4     C.sub.2 H.sub.5                                                                         CH.sub.3    F      O   O   CH.sub.3                             5     C.sub.2 H.sub.5                                                                         C.sub.2 H.sub.5                                                                            CH.sub.3                                                                              O   O   i-C.sub.3 H.sub.7                    6     C.sub.2 H.sub.5                                                                         C.sub.2 H.sub.5                                                                            F      O   S   C.sub.2 H.sub.5                      7     C.sub.2 H.sub.5                                                                         CH.sub.2 CH.sub.2 CH.sub. 3                                                                F      O   O   i-C.sub.3 H.sub.7                    8     C.sub.2 H.sub.5                                                                         CH.sub.2 CH.sub.2 CH.sub.3                                                                 F      S   O   i-C.sub.3 H.sub.7                    9     C.sub.2 H.sub.5                                                                         C.sub.2 H.sub.5                                                                            F      S   S   i-C.sub.3 H.sub.7                    10    CH.sub.3 CH.sub.3    OCH.sub.3                                                                             O   O   i-C.sub.3 H.sub.7                    ______________________________________                                    

In the practical usage of the compounds (I) as fungicides, they may be applied as such or in a formulation form such as dusts, wettable powders, oil sprays, emulsifiable concentrates, tablets, granules, fine granules, aerosols or flowables. Such formulation form can be formulated in a conventional manner by mixing at least one of the compounds (I) with an appropriate solid or liquid carrier(s) or diluent(s) and, if necessary, an appropriate adjuvant(s) (e.g. surfactants, adherents, dispersants, stabilizers) for improving the dispersibility and other properties of the active ingredient.

Examples of the solid carriers or diluents are botanical materials (e.g. flour, tobacco stalk powder, soybean powder, walnut-shell powder, vegetable powder, saw dust, bran, bark powder, cellulose powder, vegetable extract residue), fibrous materials (e.g. paper, corrugated cardboard, old rags), synthetic plastic powders, clays (e.g. kaolin, bentonite, fuller's earth), talcs, other inorganic materials (e.g. pyrophyllite, sericite, pumice, sulfur powder, active carbon) and chemical fertilizers (e.g. ammonium sulfate, ammonium phosphate, ammonium nitrate, urea, ammonium chloride).

Examples of the liquid carriers or diluents are water, alcohols (e.g. methanol, ethanol), ketones (e.g. acetone, methylethylketone), ethers (e.g. diethyl ether, dioxane, cellosolve, tetrahydrofuran), aromatic hydrocarbons (e.g. benzene, toluene, xylene, methyl naphthalene), aliphatic hydrocarbons (e.g. gasoline, kerosene, lamp oil), esters, nitriles, acid amides (e.g. dimethylformamide, dimethylacetamide), halogenated hydrocarbons (e.g. dichloroethane, carbon tetrachloride), etc.

Examples of the surfactants are alkyl sulfuric esters, alkyl sulfonates, alkylaryl sulfonates, polyethylene glycol ethers, polyhydric alcohol esters, etc. Examples of the adherents and dispersants may include casein, gelatin, starch powder, carboxymethyl cellulose, gum arabic, alginic acid, lignin, bentonite, molasses, polyvinyl alcohol, pine oil and agar. As the stabilizers, there may be used PAP (isopropyl acid phosphate mixture), tricresyl phosphate (TCP), tolu oil, epoxydized oil, various surfactants, various fatty acids and their esters, etc.

The foregoing formulations generally contain at least one of the compounds (I) in a concentration of about 1 to 95% by weight, preferably of 2.0 to 80% by weight. By using the formulations, the compounds (I) are generally applied in such amounts as 2 to 100 g per 10 are.

When only the drug-resistant strains of phytopathogenic fungi are present, the compounds (I) may be used alone. However, when the drug-sensitive strains are present together with the drug-resistant strains, their alternate use with benzimidazole, thiophanate and/or cyclic imide fungicides or their combined use with benzimidazole, thiophanate fungicides and/or cyclic imide fungicides is favorable. In such alternate or combined use, each active ingredient may be employed as such or in conventional agricultural formulation forms. In case of the combined use, the weight proportion of the compound (I) and the benzimidazole, thiophanate and/or cyclic imide fungicide may be from about 1:0.1 to 1:10.0.

Typical examples of the benzimidazole, thiophanate and cyclic imide fungicides are shown in Table 2.

                  TABLE 2                                                          ______________________________________                                         Com-                                                                           pound Structure                Name                                            ______________________________________                                                ##STR10##               Methyl 1- (butyl- carbamoyl) benz-                                             imidazol-2- yl- carbamate                       B                                                                                     ##STR11##               2-(4- Thiazolyl) benz- imidazole                C                                                                                     ##STR12##               Methyl benz- imidazol- 2-yl carbamate           D                                                                                     ##STR13##               2-(2-Furyl) benz- imidazole                     E                                                                                     ##STR14##               1,2-Bis(3- methoxy- carbonyl-2- thioureido)                                     benzene                                        F                                                                                     ##STR15##               1,2-Bis(3- ethoxy- carbonyl-2- thioureido)                                     enzene                                          G                                                                                     ##STR16##               2-(O,S Dimethyl- phosphoryl- amino)-1-                                         (3'- methoxy- carbonyl- 2'- thioureido)                                        benzene                                         H                                                                                     ##STR17##               2-(O,O Dimethyl- thio- phosphoryl-                                             amino)-1- (3'- methoxy- carbonyl- 2'-                                          thioureido) benzene                             I                                                                                     ##STR18##               N(3',5'- Dichloro- phenyl)-1,2- dimethyl-                                      cyclo- propane- 1,2-di- carbox- imide           J                                                                                     ##STR19##               3-(3',5'- Dichloro- phenyl)-1- isopropyl-                                      carbamoyl- imida- zolidin- 2,4-dione            K                                                                                     ##STR20##               3-(3',5'- Dichloro- phenyl)-5- methyl-5-                                       vinyloxa- zolidin-2,4- dione                    L                                                                                     ##STR21##               Ethyl (RS)- 3-(3',5'- dichloro- phenyl)-5-                                     ethyl-2,4- dioxo- oxazol- idine-5-                                             carboxylate                                     ______________________________________                                    

Besides, the compounds (I) may be also used in admixture with other fungicides, herbicides, insecticides, miticides, fertilizers, etc.

When the compounds (I) are used as fungicides, they may be applied in such amounts as 2 to 100 grams per 10 ares. However, this amount may vary depending upon formulation forms, application times, application methods, application sites, diseases, crops and so on, and therefore, they are not limited to said particular amounts.

Some practical embodiments of the fungicidal composition according to the invention are illustratively shown in the following Examples wherein % and part(s) are by weight.

FORMULATION EXAMPLE 1

Two parts of Compound No. 1, 88 parts of clay and 10 parts of talc are thoroughly pulverized and mixed together to obtain a dust formulation containing 2% of the active ingredients.

FORMULATION EXAMPLE 2

Thirty parts of Compound No. 1, 45 parts of diatomaceous earth, 20 parts of white carbon, 3 parts of sodium laurylsulfate as a wetting agent and 2 parts of calcium ligninsulfonate as a dispersing agent are mixed while being powdered to obtain a wettable powder formulation containing 30% of the active ingredients.

FORMULATION EXAMPLE 3

Fifty parts of Compound No. 1, 45 parts of diatomaceous earth, 2.5 parts of calcium alkylbenzenesulfonate as a wetting agent and 2.5 parts of calcium ligninsulfonate as a dispersing agent are mixed while being powdered to obtain a wettable powder formulation containing 50% of the active ingredients.

FORMULATION EXAMPLE 4

Ten parts of Compound No. 1, 80 parts of cyclohexanone and 10 parts of polyoxyethylene alkylaryl ether as an emulsifier are mixed together to obtain an emulsifiable concentrate formulation containing 10% of the active ingredient.

FORMULATION EXAMPLE 5

One part of Compound No. 1, 1 part of Compound I, 88 parts of clay and 10 parts of talc are thoroughly pulverized and mixed together to obtain a dust formulation containing 2% of the active ingredient.

FORMULATION EXAMPLE 6

Twenty parts of Compound No. 1, 10 parts of Compound J, 45 parts of diatomaceous earth, 20 parts of white carbon, 3 parts of sodium laurylsulfate as a wetting agent and 2 parts of calcium ligninsulfonate as a dispersing agent are mixed while being powdered to obtain a wettable powder formulation containing 30% of the active ingredients.

FORMULATION EXAMPLE 7

Ten parts of Compound No. 1, 40 parts of Compound A, 45 parts of diatomaceous earth, 2.5 parts of calcium alkylbenzenesulfonate as a wetting agent and 2.5 parts of calcium ligninsulfonate as a dispersing agent are mixed while being powdered to obtain a wettable powder formulation containing 30% of the active ingredients.

Typical test data indicating the excellent fungicidal activity of the compounds of the formula (I) are shown below. The compounds used for comparison are as follows:

    ______________________________________                                         Compound             Remarks                                                   ______________________________________                                         Swep                                                                            ##STR22##           Commercially available herbicide                          Chlorpropham                                                                    ##STR23##           Commercially available herbicide                          Barban                                                                          ##STR24##           Commercially available herbicide                          CEPC                                                                            ##STR25##           Commercially available herbicide                          Propham                                                                         ##STR26##           Commercially available herbicide                          Chlorbufam                                                                      ##STR27##           Commercially available herbicide                          Benomyl                                                                         ##STR28##           Commercially available fungicide                          Thiophanate-methyl                                                              ##STR29##           Commercially available fungicide                          Carbendazim                                                                     ##STR30##           Commercially available fungicide                          ______________________________________                                    

EXPERIMENT 1 Protective activity test on powdery mildew of cucumber (Sphaerotheca fuliginea)

A flower pot of 90 ml volume is filled with sandy soil, and seeds of cucumber (var: Sagami-hanjiro) are sowed therein. Cultivation is carried out in a greenhouse for 8 days. Onto the resulting seedlings having cotyledons, the test compound formulated in an emulsifiable concentrate or wettable powder and diluted with water is sprayed at a rate of 10 ml per pot. Then, the seedlings are inoculated with a spore suspension of the drug-resistant or drug-sensitive strain of Sphaerotheca fuliginea by spraying and further cultivated in the greenhouse. Ten days thereafter, the infectious state of the plants is observed. The degree of damage is determined in the following manner, and the results are shown in Table 3.

The leaves examined are measured for a percentage of infected area and classified into the corresponding disease indices, 0, 0.5, 1, 2, 4:

    ______________________________________                                         Disease index Percentage of infected area                                      ______________________________________                                         0             No infection                                                     0.5           Infected area of less than 5%                                    1             Infected area of less than 20%                                   2             Infected area of less than 50%                                   4             Infected area of not less than 50%                               ______________________________________                                    

The disease severity is calculated according to the following equation: ##EQU1##

The prevention value is calculated according to the following equation: ##EQU2##

                  TABLE 3                                                          ______________________________________                                                                Prevention Prevention                                                          value when value when                                             Concentration                                                                               inoculated inoculated                                             of active    with drug- with drug-                                   Compound  ingredient   resistant  sensitive                                    No.       (ppm)        strain (%) strain (%)                                   ______________________________________                                         1         200          100        0                                            Swep      200          0          0                                            Chlorpropham                                                                             200          0          0                                            Barban    200          25         0                                            CEPC      200          0          0                                            Propham   200          0          0                                            Chlorbufam                                                                               200          0          0                                            Benomyl   200          0          100                                          Thiophanate-                                                                             200          0          100                                          methyl                                                                         Carbendazim                                                                              200          0          100                                          ______________________________________                                    

As understood from the results shown in Table 3, the compound (I) of the invention shows an excellent preventive effect on the drug-resistant strain but does not show any preventive effect on the tested drug-sensitive strain. To the contrary, commercially available known fungicides such as Benomyl, Thiophanate-methyl and Carbendazim show a notable controlling effect on the drug-sensitive strain but not on the drug-resistant strain. Other tested compounds structurally similar to the compounds (I) do not show any fungicidal activity on the drug-sensitive strain and the drug-resistant strain.

EXPERIMENT 2 Preventive effect on cerospora leaf spot of sugarbeet (Cercospora beticola)

A flower pot of 90 ml volume is filled with sandy soil, and seeds of sugarbeet (var: Detroit dark red) are sowed therein. Cultivation is carried out in a greenhouse for 20 days. Onto the resulting seedlings, the test compound formulated in an emulsifiable concentrate or wettable powder and diluted with water is sprayed at a rate of 10 ml per pot. Then, the seedlings are inoculated with a spore suspension of the drug-resistant or drug-sensitive strain of Cercospora beticola by spraying. The pot is covered with a polyvinyl chloride sheet to make a condition of high humidity, and cultivation is continued in the greenhouse for 10 days. The degree of damage is determined in the same manner as in Experiment 1, and the results are shown in Table 4.

                  TABLE 4                                                          ______________________________________                                                                Prevention Prevention                                                          value when value when                                             Concentration                                                                               inoculated inoculated                                             of active    with drug- with drug-                                   Compound  ingredient   resistant  sensitive                                    No.       (ppm)        strain (%) strain (%)                                   ______________________________________                                         1         500          100        0                                            Swep      200          0          0                                            Chlorpropham                                                                             200          0          0                                            Barban    200          34         0                                            CEPC      200          0          0                                            Propham   200          0          0                                            Chlorbufam                                                                               200          0          0                                            Benomyl   200          0          100                                          Thiophanate-                                                                             200          0          100                                          methyl                                                                         Carbendazim                                                                              200          0          100                                          ______________________________________                                    

As understood from the results shown in Table 4, the compound (I) of the invention shows an excellent preventive effect on the drug-resistant strain but does not show any preventive effect on the tested drug-sensitive strain. To the contrary, commercially available known fungicides such as Benomyl, Thiophanate-methyl and Carbendazim show a notable controlling effect on the drug-sensitive strain but not on the drug-resistant strain. Other tested compounds structurally similar to the compounds (I) do not show any fungicidal activity on the drug-sensitive strain and the drug-resistant strain.

EXPERIMENT 3 Preventive effect on scab of pear (Venturia nashicola)

A plastic pot of 90 ml volume is filled with sandy soil, and seeds of pear (var: Chojuro) are sowed therein. Cultivation is carried out in a greenhouse for 20 days. Onto the resulting seedlings, the test compound formulated in an emulsifiable concentrate or wettable powder and diluted with water is sprayed at a rate of 10 ml per pot. Then, the seedlings are inoculated with a spore suspension of the drug-resistant or drug-sensitive strain of Venturia nashicola by spraying. The resulting plants are placed at 20° C. under a condition of high humidity for 3 days and then at 20° C. under irradiation with a fluorescent lamp for 20 days. The degree of damage is determined in the same manner as in Experiment 1, and the results are shown in Table 5.

                  TABLE 5                                                          ______________________________________                                                                Prevention Prevention                                                          value when value when                                             Concentration                                                                               inoculated inoculated                                             of active    with drug- with drug-                                   Compound  ingredient   resistant  sensitive                                    No.       (ppm)        strain (%) strain (%)                                   ______________________________________                                         1         500          100         0                                           Benomyl   200          0          100                                          Thiophanate-                                                                             200          0          100                                          methyl                                                                         ______________________________________                                    

As understood from the results shown in Table 5, the compound (I) of the invention shows an excellent preventive effect on the drug-resistant strain but does not show any preventive effect on the tested drug-sensitive strain. To the contrary, commercially available known fungicides such as Benomyl and Thioophanate-methyl show a notable controlling effect on the drug-sensitive strain but not on the drug-resistant strain.

EXPERIMENT 4 Preventive effect on brown leaf-spot of peanut (Cercospora arachidicola)

Plastic pots of 90 ml volume were filled with sandy soil, and seeds of peanut (var: Chiba hanryusei) were sowed therein. Cultivation was carried out in a greenhouse for 14 days. Onto the resulting seedlings, the test compound formulated in an emulsifiable concentrate or wettable powder and diluted with water was sprayed at a rate of 10 ml per pot. Then, the seedlings were inoculated with a spore suspension of the drug-resistant or drug-sensitive strain of Cercospora arachidicola by spraying. The resulting plants were covered with a polyvinyl chloride sheet to make a condition of humidity and cultivated in the greenhouse for 10 days. The degree of damage was determined in the same manner as in Experiment 1, and the results are shown in Table 6.

                  TABLE 6                                                          ______________________________________                                                                Prevention Prevention                                                          value when value when                                             Concentration                                                                               inoculated inoculated                                             of active    with drug- with drug-                                   Compound  ingredient   resistant  sensitive                                    No.       (ppm)        strain (%) strain (%)                                   ______________________________________                                         1         500          100         0                                           Benomyl   200          0          100                                          Thiophanate-                                                                             200          0          100                                          methyl                                                                         ______________________________________                                    

As understood from the results shown in Table 6, the compound of the formula (I) of the invention shows an excellent preventive effect on the drug-resistant strain but does not show any preventive effect on the tested drug-sensitive strain. To the contrary, commercially available known fungicides such as Benomyl and Thiophanate-methyl show a notable controlling effect on the drug-sensitive strain but not on the drug-resistant strain.

EXPERIMENT 5 Preventive effect on gray mold of cucumber (Botrytis cinerea)

Plastic pots of 90 ml volume are filled with sandy soil, and seeds of cucumber (var: Sagami-hanjiro) are sowed therein. Cultivation is carried out in a greenhouse for 8 days to obtain cucumber seedlings expanding cotyledons. Onto the resulting seedlings, the test compound formulated in an emulsifiable concentrate or wettable powder and diluted with water is sprayed at a rate of 10 ml per pot. After air-drying, the seedlings are inoculated with mycelial disks (5 mm in diameter) of the drug-resistant or drug-sensitive strain of Botrytis cinerea by putting them on the leaf surfaces. After the plants are infected by incubating under high humidity at 20° C. for 3 days, the rates of disease severity are observed. The degree of damage is determined in the same manner as in Experiment 1, and the results are shown in Table 7.

                  TABLE 7                                                          ______________________________________                                                                Prevention Prevention                                                          value when value when                                             Concentration                                                                               inoculated inoculated                                             of active    with drug- with drug-                                   Compound  ingredient   resistant  sensitive                                    No.       (ppm)        strain (%) strain (%)                                   ______________________________________                                         1         200          100         0                                           Benomyl   200          0          100                                          Thiophanate-                                                                             200          0          100                                          methyl                                                                         ______________________________________                                    

As understood from the results shown in Table 7, the compound (I) of the invention shows an excellent preventive effect on the drug-resistant strain but does not show any preventive effect on the tested drug-sensitive strain. To the contrary, commercially available known fungicides such as Benomyl and Thiophanate-methyl show a notable controlling effect on the drug-sensitive strain but not on the drug-resistant strain.

EXPERIMENT 6 Preventive effect on gummy stem blight of cucumber (Mycosphaerella melonis)

Plastic pots of 90 ml volume were filled with sandy soil, and seeds of cucumber (var: Sagami-hanjiro) were sowed therein. Cultivation was carried out in a greenhouse for 8 days to obtain cucumber seedlings expanding cotyledons. Onto the resulting seedlings, the test compound formulated in an emulsifiable concentrate or wettable powder and diluted with water was sprayed at a rate of 10 ml per pot. After air-drying, the seedlings were inoculated with mycelial disks (5 mm in diameter) of the drug-resistant or drug-sensitive strain of Mycosphaerella melonis by putting them on the leaf surfaces. After the plants were infected by incubating under high humidity at 25° C. for 4 days, the rates of disease severity were observed. The degree of damage was determined in the same manner as in Experiment 1, and the results are shown in Table 8.

                  TABLE 8                                                          ______________________________________                                                                Prevention Prevention                                                          value when value when                                             Concentration                                                                               inoculated inoculated                                             of active    with drug- with drug-                                   Compound  ingredient   resistant  sensitive                                    No.       (ppm)        strain (%) strain (%)                                   ______________________________________                                         1         200          100         0                                           Benomyl   200          0          100                                          Thiophanate-                                                                             200          0          100                                          methyl                                                                         ______________________________________                                    

As understood from the results shown in Table 8, the compound of the formula (I) of the invention shows an excellent preventive effect on the drug-resistant strain but does not show any preventive effect on the tested drug-sensitive strain. To the contrary, commercially available known fungicides such as Benomyl and Thiophanate-methyl show a notable controlling effect on the drug-sensitive strain but not on the drug-resistant strain.

EXPERIMENT 7 Preventive effect on green mold of orange (Penicillium italicum)

Fruits of orange (var: Unshu) were washed with water and dried in the air. The fruits were immersed in a solution of the test compound prepared by diluting an emulsifiable concentrate comprising the test compound with water for 1 minute. After drying in the air, the fruits were inoculated with a spore suspension of the drug-resistant or drug-sensitive strain of Penicillium italicum by spraying and placed in a room of high humidity for 14 days. The degree of damage was determined in the following manner:

The fruits examined were measured for a percentage of infected area and classified into the corresponding indices, 0, 1, 2, 3, 4, 5:

    ______________________________________                                         Disease index Percentage of infected area                                      ______________________________________                                         0             No infection                                                     1             Infected area of less than 20%                                   2             Infected area of less than 40%                                   3             Infected area of less than 60%                                   4             Infected area of less than 80%                                   5             Infected area of not less than 80%                               ______________________________________                                    

Calculation of the degree of damage and the prevention value was made as in Experiment 1.

The results are shown in Table 9.

                  TABLE 9                                                          ______________________________________                                                                Prevention Prevention                                                          value when value when                                             Concentration                                                                               inoculated inoculated                                             of active    with drug- with drug-                                   Compound  ingredient   resistant  sensitive                                    No.       (ppm)        strain (%) strain (%)                                   ______________________________________                                         1         500          100         0                                           Benomyl   200          0          100                                          Thiophanate-                                                                             200          0          100                                          methyl                                                                         ______________________________________                                    

As understood from the results shown in Table 9, the compound of the formula (I) of the invention shows an excellent preventive effect on the drug-resistant strain but does not show any preventive effect on the tested drug-sensitive strain. To the contrary, commercially available known fungicides such as Benomyl and Thiophanate-methyl show a notable controlling effect on the drug-sensitive strain but not on the drug-resistant strain.

EXPERIMENT 8 Phytotoxicity on crop plants

Plastic pots of 150 ml volume were filled with sandy soil, and seeds of wheat (var: Norin No. 61), apple (var: Kogyoku) and peanut (var: Chiba hanryusei) were sowed therein. Cultivation was carried out in a greenhouse. Onto the resulting seedlings, the test compound formulated in an emulsifiable concentrate or wettable powder and diluted with water was sprayed. After cultivation in the greenhouse for an additional 10 days, the phytotoxicity was examined on the following criteria:

    ______________________________________                                         Extent    Observation                                                          ______________________________________                                         -         No abnormality                                                       +         Abnormality due to phytotoxicity observed                                      in a part of crop plants                                             ++        Abnormality due to phytotoxicity observed                                      in entire crop plants                                                +++       Crop plants withered due to phytotoxicity                            ______________________________________                                    

The results are shown in Table 10.

                  TABLE 10                                                         ______________________________________                                                  Concentration                                                                  of active                                                             Compound ingredient  Phytotoxicity                                             No.      (ppm)       Wheat     Apple Peanut                                    ______________________________________                                         1        1000        -         -     -                                         Barban   1000        -         ++    ++                                        CEPC     1000        -         ++    ++                                        Swep     1000        ++        ++    +                                         ______________________________________                                    

As understood from the results shown in Table 10, the compound of the formula (I) of the invention produce no material phytotoxicity, while commercially available herbicides having a chemical structure similar thereto produces considerable phytotoxicity.

EXPERIMENT 9 Preventive effect on powdery mildew of cucumber (Sphaerotheca fuliginea)

A plastic pot of 90 ml volume was filled with sandy soil, and seeds of cucumber (var: Sagami-hanjiro) were sowed therein. Cultivation was carried out in a greenhouse for 8 days. Onto the resulting seedlings having cotyledons, the test compound(s) formulated in emulsifiable concentrate or wettable powder and diluted with water were sprayed at a rate of 10 ml per pot. Then, the seedlings were inoculated with a mixed spore suspension of the drug-resistant and drug-sensitive strain of Sphaerotheca fuliginea by spraying and further cultivated in the greenhouse. Ten days thereafter, the infectious state of the plants was observed. The degree of damage was determined in the same manner as in Experiment 1, and the results are shown in Table 11.

                  TABLE 11                                                         ______________________________________                                                       Concentration of                                                                            Prevention                                                        active ingredient                                                                           value                                               Compound No.  (ppm)        (%)                                                 ______________________________________                                         1             100           42                                                 1              20           0                                                  A             100           45                                                 A              20           12                                                 B             500           42                                                 B             100           10                                                 C             100           42                                                 C              20           8                                                  D             500           36                                                 D             100           0                                                  E             100           44                                                 E              20           10                                                 F             100           43                                                 F              20           8                                                  G             100           42                                                 G              20           8                                                  H             100           40                                                 H              20           5                                                  1 + A         20 + 20      100                                                 1 + B         20 + 20      100                                                 1 + C         20 + 20      100                                                 1 + D         20 + 20      100                                                 1 + E         20 + 20      100                                                 1 + F         20 + 20      100                                                 1 + G         20 + 20      100                                                 1 + H         20 + 20      100                                                 ______________________________________                                    

As understood from the results shown in Table 11, the combined use of the compound of the formula (I) of the invention with benzimidazole, thiophanate and/or cyclic imide fungicides show much more excellent preventive effect than their sole use.

EXPERIMENT 10 Preventive effect on gray mold of tomato (Botrytis cinerea)

A plastic pot of 90 ml volume is filled with sandy soil, and seeds of tomato (var: Fukuju No. 2) are sowed therein. Cultivation is carried out in a greenhouse for 4 weeks. Onto the resulting seedlings at the 4-leaf stage, the test compound(s) formulated in an emulsifiable concentrate or wettable powder and diluted with water are sprayed at a rate of 10 ml per pot. Then, the seedlings are inoculated with a mixed spore suspension of the drug-resistant and drug-sensitive strain of Botrytis cinerea by spraying and placed at 20° C. in a room of high humidity for 5 days. The degree of damage is determined in the same manner as in Experiment 1, and the results are shown in Table 12.

                  TABLE 12                                                         ______________________________________                                                       Concentration of                                                                            Prevention                                                        active ingredient                                                                           value                                               Compound No.  (ppm)        (%)                                                 ______________________________________                                         1             100          38                                                  1              20           0                                                  I             100          48                                                  I              20          22                                                  J             500          46                                                  J             100          18                                                  K             100          42                                                  K              20          15                                                  L             500          42                                                  L             100          12                                                  1 + I         20 + 50      100                                                 1 + J         20 + 50      100                                                 1 + K         20 + 50      100                                                 1 + L         20 + 50      100                                                 ______________________________________                                    

As understood from the results shown in Table 12, the combined use of the compound (I) of the invention with benzimidazole, thiophanate and/or cyclic imide fungicides show much more excellent preventive effect than their sole use. 

What is claimed is:
 1. A compound of the formula: ##STR31## wherein R₁, R₂ and R₃ are, the same or different, each a lower alkyl group, X is a halogen atom or a lower alkyl group and A and B are each an oxygen atom.
 2. The compound according to claim 1, wherein R₁ and R₂ are each a lower alkyl group, R₃ is an isopropy group, X is a fluorine atom and A and B are each an oxygen atom.
 3. A compound of the formula: ##STR32##
 4. A fungicidal composition which comprises as an active ingredient a fungicidally effective amount of a compound of the formula: ##STR33## wherein R₁, R₂ and R₃ are, the same or different, each a lower alkyl group, X is a halogen atom or a lower alkyl group and A and B are each an oxygen atom, and an inert carrier or diluent.
 5. The fungicidal composition according to claim 4, which further comprises as an additional active ingredient(s) a benzimidazole, thiophanate and/or cyclic imide fungicide(s).
 6. The fungicidal composition according to claim 5, wherein the benzimidazole fungicide is chosen from methyl 1-(butylcarbamoyl)benzimidazol-2-ylcarbamate, 2-(2-furyl)benzimidazole, 2-(4-thiazolyl)benzimidazole and methyl benzimidazol-2-ylcarbamate, the thiophanate fungicide is chosen from 1,2-bis(3-methoxycarbonyl-2-thioureido)benzene, 1,2-bis(3-ethoxycarbonyl-2-thioureido)benzene, 2-(O,S-dimethylphosphorylamino)-1-(3'-methoxycarbonyl-2'-thioureido)benzene and 2-(O,O-dimethylthiophosphorylamino)-1-(3'-methoxycarbonyl-2'-thioureido)benzene, and the cyclic imide fungicide is chosen from 3-(3',5'-dichlorophenyl)-1,2-dimethylcyclopropane-1,2-dicarboximide, 3-(3',5'-dichlorophenyl)-1-isopropylcarbamoylimidazolidine-2,4-dione, 3-(3',5'-dichlorophenyl)-5-methyl-5-vinyloxazolidine-2,4-dione and ethyl (RS)-3-(3',5'-dichlorophenyl)-5-methyl-2,4-dioxooxazolidine-5-carboxylate.
 7. A method for controlling drug-resistant strains of plant pathogenic fungi which comprises applying a fungicidally effective amount of at least one of the compounds of the formula: ##STR34## wherein R₁, R₂, R₃, X, A and B are each as defined in claim 1, to said drug-resistant strains of plant pathogenic fungi.
 8. A method for controlling drug-resistant strains of plant pathogenic fungi which comprises applying thereto a fungicidally effective amount of a mixture of at least one of the compounds of the formula: ##STR35## wherein R₁, R₂, R₃, X, A and B are each as defined in claim 1, and at least one of benzimidazole, thiophanate and cyclic imide fungicides. 